1. Field of the Invention
The present invention relates generally to doors installed on enclosed trucks or trailer and, more particularly, to truck and trailer doors that are adapted for opening by being moved to a position above the door threshold.
2. Description of the Prior Art
Doors for enclosed trucks, and especially enclosed trailer doors, are often doors that are adapted for opening by being moved to a position above the door threshold. Such overhead doors are generally comprised of a plurality of articulated panel units that have laterally located rollers that ride in laterally located channels as the overhead door is opened and closed. The panels are connected to each other by hinges. Each channel has a vertical portion for keeping the articulated panels in a vertical orientation when the door is closed. Also, each channel has a horizontal portion for retaining the articulated panels in a horizontal orientation when the door is open. Unfortunately, with this type of overhead door, rollers and hinges for the articulated panels are highly susceptible to wear and tear and often need repair or replacement. In this respect, it would be desirable if an overhead door were provided for an enclosed truck or trailer that does not include a plurality of articulated panels connected together by hinges. Also, it would be desirable if an overhead door were provided for an enclosed truck or tr28 ailer which does not include a plurality of rollers associated with each of a plurality of articulated door panels.
The most important factors causing the wear and tear of the hinges of the articulated door panels and the lateral rollers are the vibrations and the road shocks that are transmitted to the stack of door panels and the rollers for each door panel when they are in the vertical portions of the lateral roller channels when the truck or trailer is in motion. Much of such vibration and road shock damage to the overhead door could be reduced or eliminated if the vertical stack of hinged door panels and the vertical stack of lateral rollers could be eliminated. In this respect, it would be desirable if an overhead door were provided for an enclosed truck or trailer that did not include a vertical stack of hinged door panels and did not include a vertical stack of lateral rollers.
In structures that bear stresses and strains, it is well known that the triangle is an excellent structural form for withstanding stresses and strains. In this respect, it would be desirable if an overhead door were provided for an enclosed truck or trailer that employed triangular construction forms.
Another contributing factor to damage experienced by an overhead door for a truck or trailer is the weight of the overhead door. A heavy overhead door tends to experience considerable vibration and road shock damage due to large inertial forces engendered by the heavy weight of the door. To lessen damage of vibration and road shock to an overhead door, it would be desirable if the overhead door were lightweight.
Lifting an overhead door for a truck or trailer may require considerable effort. The door must be lifted against the pull of gravity. To lessen the lifting effort, it would be desirable if the overhead door contained components which provide a lifting force to assist a person in lifting the overhead door.
Throughout the years, a number of innovations have been developed relating to doors for containers, such as tracks and trailers, and the following U.S. patents are representative of some of those innovations: U.S. Pat. Nos. 3,596,403; 3,934,635; 3,950,894; 4,057,170; and 5,016,393. More specifically, U.S. Pat. Nos. 3,596,403 and 4,057,170 disclose trailer doors that open sideways, not overhead. Such side opening doors require two doors at the back of each trailer, one door for the left side and one door for the right side. To avoid the complexity of two doors, it would be desirable if only one truck or trailer door were employed.
U.S. Pat. No. 3,934,635 discloses an overhead door for a trailer that employs a plurality of hinged door panels that have laterally disposed rollers as described above. In addition, the panels are counterbalanced by a spring which is wound by gears that cooperate with racks on the horizontal portions of the tracks on which the panels are movably supported. Although the use of a counterbalancing device is desirable, the use of gears which cooperate with racks may not be. Rotating gears present structures that need be periodically lubricated and may be prone to squeaking if not properly lubricated. In this respect, it would be desirable if an overhead door were provided for an enclosed truck or trailer which provided counterbalancing without the use of gears.
U.S. Pat. Nos. 3,950,894 and 5,016,393 may be of interest for their disclosure of particular door constructions. However, none of the doors disclosed in these patents are for overhead doors for trucks or trailers.
Thus, while the foregoing body of prior art indicates it to be well known to use overhead doors for trucks and trailers, the prior art described above does not teach or suggest a overhead door apparatus which has the following combination of desirable features: (1) does not include a plurality of articulated panels connected together by hinges; (2) does not include a plurality of rollers associated with each of a plurality of articulated door panels; (3) does not include a vertical stack of hinged door panels and does not include a vertical stack of lateral rollers; (4) employs triangular construction forms; (5) is lightweight; (6) contains components which provide a lifting force to assist a person in lifting the overhead door; (7) employs only one door panel; and (8) provides counterbalancing of a single door panel without the use of gears. The foregoing desired characteristics are provided by the unique overhead door apparatus of the present invention as will be made apparent from the following description thereof. Other advantages of the present invention over the prior art also will be rendered evident.